Gas sensor

ABSTRACT

A gas sensor includes: a substrate; a first conductor and a second conductor that are disposed on the substrate; an insulating layer; and an adsorbent layer. The insulating layer covers the first conductor and the second conductor, and has a first opening that allows a part of a surface of the first conductor to be exposed therethrough and a second opening that allows a part of a surface of the second conductor to be exposed therethrough. The adsorbent layer contains a conductive material and an organic adsorbent that can adsorb a gas. The adsorbent layer is in contact with the first conductor and the second conductor respectively through the first opening and the second opening.

TECHNICAL FIELD

The present disclosure relates to a gas sensor.

BACKGROUND ART

Gas sensors are known as equipment for detecting a gas. The gas sensorsmake it possible to detect a gas easily.

As shown in FIG. 11, a substance detection sensor 300 to detect a gas isdescribed in Patent Literature 1. The substance detection sensor 300 isprovided with a conductive layer 330, a first electrode 320 and a secondelectrode 325. The conductive layer 330 covers each of the firstelectrode 320 and the second electrode 325.

Use of the substance detection sensor 300 makes it possible to detect agas as follows. When a gas comes in contact with the conductive layer330, the conductive layer 330 is swollen. This changes an electricresistance value of the conductive layer 330. It is possible to detectthe gas by measuring the change in the electric resistance value of theconductive layer 330.

CITATION LIST Patent Literature

Patent Literature 1: WO 2008/084582 A1

SUMMARY OF INVENTION Technical Problem

In some cases, the substance detection sensor 300 described in PatentLiterature 1 fails to detect a gas well enough when the gas has a lowconcentration.

The present disclosure is intended to provide a technology for detectinga gas more reliably.

Solution to Problem

That is, the present disclosure provides a gas sensor including:

a substrate;

a first conductor and a second conductor that are disposed on thesubstrate;

an insulating layer that covers the first conductor and the secondconductor, and that has a first opening that allows a part of a surfaceof the first conductor to be exposed therethrough and a second openingthat allows a part of a surface of the second conductor to be exposedtherethrough; and

an adsorbent layer that contains a conductive material and an organicadsorbent that can adsorb a gas, and that is in contact with the firstconductor and the second conductor respectively through the firstopening and the second opening.

Advantageous Effects of Invention

The gas sensor of the present disclosure makes it possible to detect agas more reliably.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a gas sensor according to Embodiment 1 of thepresent disclosure.

FIG. 2 is a cross-sectional view of the gas sensor shown in FIG. 1,taken along the line II-II.

FIG. 3 is a diagram to explain positions of a plurality of firstopenings and positions of a plurality of second openings in the gassensor shown in FIG. 1.

FIG. 4 is a plan view of a gas sensor assembly according to oneembodiment of the present disclosure.

FIG. 5 is a plan view of a gas sensor according to a modification ofEmbodiment 1 of the present disclosure.

FIG. 6 is a cross-sectional view of the gas sensor shown in FIG. 5,taken along the line VI-VI.

FIG. 7 is a plan view of a gas sensor according to Embodiment 2.

FIG. 8 is a plan view of a gas sensor according to Embodiment 3.

FIG. 9 is a graph showing a rate of change in electric resistance of anadsorbent layer in each of Samples 1 to 5.

FIG. 10 is a graph showing a rate of change in electric resistance of anadsorbent layer in each of Samples 2, 6 and 7.

FIG. 11 is a plan view of a conventional gas sensor.

DESCRIPTION OF EMBODIMENTS

The gas sensor according to a first embodiment of the present disclosureincludes:

a substrate;

a first conductor and a second conductor that are disposed on thesubstrate;

an insulating layer that covers the first conductor and the secondconductor, and that has a first opening that allows a part of a surfaceof the first conductor to be exposed therethrough and a second openingthat allows a part of a surface of the second conductor to be exposedtherethrough; and

an adsorbent layer that contains a conductive material and an organicadsorbent that can adsorb a gas, and that is in contact with the firstconductor and the second conductor respectively through the firstopening and the second opening.

According to the first embodiment, the adsorbent layer changes in volumewhen the organic adsorbent adsorbs a gas. To be specific, the adsorbentlayer expands or shrinks. The change in volume of the adsorbent layerchanges the positional relationship between the conductive materials inthe adsorbent layer. Thereby, electric current paths in the adsorbentlayer change. In the gas sensor, the first conductor has a surface thatis covered with the insulating layer, and no electric current passesfrom that surface to the adsorbent layer. The second conductor has asurface that is covered with the insulating layer, and no electriccurrent passes from that surface to the adsorbent layer. That is, thenumber of the electric current paths in the adsorbent layer is small.Therefore, the electric current paths change significantly due to thechange in the positional relationship between the conductive materials.The significant change in the electric current paths changes theelectric resistance of the adsorbent layer significantly. Thesignificant change in the electric resistance of the adsorbent layermakes it possible to detect a gas more reliably.

In a second embodiment of the present disclosure according to, forexample, the first embodiment, the insulating layer has a plurality ofthe first openings and a plurality of the second openings. The secondembodiment makes it possible to detect stably the change in the electricresistance of the adsorbent layer caused by the change in the electriccurrent paths. Thereby, a gas can be detected stably.

In a third embodiment of the present disclosure according to, forexample, the gas sensor of the second embodiment, the first openings arearranged in a circular arc shape and the second openings are arranged ina circular arc shape. The third embodiment makes it possible to detectstably the change in the electric resistance of the adsorbent layercaused by the change in the electric current paths. Thereby, a gas canbe detected stably.

In a fourth embodiment of the present disclosure according to, forexample, the gas sensor of the third embodiment, the adsorbent layer hasa circular shape or a ring shape when viewed in plane, the firstopenings are positioned on a virtual circle that is in a concentricrelationship with a virtual circle determined by an outer periphery ofthe adsorbent layer when the adsorbent layer is viewed in plane, and thesecond openings are positioned on a virtual circle that is in aconcentric relationship with the virtual circle determined by the outerperiphery of the adsorbent layer. According to the fourth embodiment,when the adsorbent layer adsorbs a gas, the adsorbent layer expands orshrinks in a radial direction of the virtual circle determined by theouter periphery of the adsorbent layer. The first openings arepositioned on the virtual circle that is in a concentric relationshipwith the virtual circle determined by the outer periphery of theadsorbent layer. Furthermore, the second openings are positioned on thevirtual circle that is in a concentric relationship with the virtualcircle determined by the outer periphery of the adsorbent layer.Therefore, the variation in the change in the electric current paths isinhibited when the adsorbent layer expands or shrinks. This makes itpossible to detect stably the change in the electric resistance of theadsorbent layer caused by the change in the electric current paths.Thereby, a gas can be detected stably.

In a fifth embodiment of the present disclosure according to, forexample, the gas sensor of the fourth embodiment, one selected from thefirst openings and one selected from the second openings are positionedon one of a plurality of virtual straight lines extending radially froma center of the virtual circle determined by the outer periphery of theadsorbent layer. The fifth embodiment makes it possible to detect a gasmore stably.

In a sixth embodiment of the present disclosure according to, forexample, the gas sensor of the second embodiment, the first openings arearranged linearly and the second openings are arranged linearly. Thesixth embodiment makes it possible to detect stably the change in theelectric resistance of the adsorbent layer caused by the change in theelectric current paths. Thereby, a gas can be detected stably.

In a seventh embodiment of the present disclosure according to, forexample, the gas sensor of the sixth embodiment, the adsorbent layer hasa rectangular shape when viewed in plane, the first openings arearranged along a direction in which at least one selected from aplurality of outlines constituting an outer periphery of the adsorbentlayer extends when the adsorbent layer is viewed in plane, and thesecond openings are arranged along a direction in which the firstopenings are arranged. According to the seventh embodiment, when theadsorbent layer adsorbs a gas, the adsorbent layer expands or shrinks indirections in which the outlines constituting the outer periphery of theadsorbent layer extend respectively. The first openings are arrangedalong the direction in which at least one of the outlines constitutingthe outer periphery of the adsorbent layer extends. Furthermore, thesecond openings are arranged along the direction in which the firstopenings are arranged. Therefore, the variation in the change in theelectric current paths is inhibited when the adsorbent layer expands orshrinks. This makes it possible to detect stably the change in theelectric resistance of the adsorbent layer caused by the change in theelectric current paths. Thereby, a gas can be detected stably.

In an eighth embodiment of the present disclosure according to, forexample, the gas sensor of any one of the first embodiment to theseventh embodiment, an entirety of the first opening overlaps with thefirst conductor when viewed in plane, and an entirety of the secondopening overlaps with the second conductor when viewed in plane. Theeighth embodiment makes it possible to detect stably the change in theelectric resistance of the adsorbent layer caused by the change in theelectric current paths. Thereby, a gas can be detected stably.

In a ninth embodiment of the present disclosure according to, forexample, the gas sensor of any one of the first embodiment to the eighthembodiment, the organic adsorbent contains at least one selected fromthe group consisting of polyalkylene glycols, polyesters, silicones,glycerols, nitriles, dicarboxylic acid monoesters and aliphatic amines.According to the ninth embodiment, the organic adsorbent can adsorb agas easily.

In a tenth embodiment of the present disclosure according to, forexample, the gas sensor of any one of the first embodiment to the ninthembodiment, the conductive material contains carbon black. According tothe tenth embodiment, the electric resistance of the adsorbent layerchanges more significantly when the organic adsorbent changes in volume.Thereby, a gas can be detected more reliably.

In an eleventh embodiment of the present disclosure according to, forexample, the gas sensor of the tenth embodiment, a ratio of a weight ofthe carbon black to a weight of the adsorbent layer is in a range of0.25 to 0.95. According to the eleventh embodiment, an electric currentpasses easily to the adsorbent layer from the first conductor or thesecond conductor. Thereby, the electric resistance of the adsorbentlayer can be measured easily.

In a twelfth embodiment of the present disclosure according to, forexample, the gas sensor of any one of the first embodiment to theeleventh embodiment, each of the first opening and the second openinghas an area in a range of 0.2 to 2000 μm² when viewed in plane.According to the twelfth embodiment, since the number of the electriccurrent paths in the adsorbent layer is sufficiently small, the electricresistance of the adsorbent layer changes more significantly due to thechange in the electric current paths. Thereby, a gas can be detectedmore reliably. Moreover, an electric current passes easily to theadsorbent layer from the first conductor or the second conductor.Thereby, the electric resistance of the adsorbent layer can be measuredeasily.

In a thirteenth embodiment of the present disclosure according to, forexample, the gas sensor of any one of the first embodiment to thetwelfth embodiment, each of the first opening and the second opening hasa circular shape when viewed in plane, and each of the first opening andthe second opening has a diameter in a range of 0.5 to 50 μm. Accordingto the thirteenth embodiment, since the number of the electric currentpaths in the adsorbent layer is sufficiently small, the electricresistance of the adsorbent layer changes more significantly due to thechange in the electric current paths. Thereby, a gas can be detectedmore reliably. Moreover, an electric current passes easily to theadsorbent layer from the first conductor or the second conductor.Thereby, the electric resistance of the adsorbent layer can be measuredeasily.

Hereinafter, the embodiments of the present disclosure are describedwith reference to the drawings. The present disclosure is not limited tothe following embodiments.

Embodiment 1

As shown in FIG. 1 and FIG. 2, a gas sensor 100 according to the presentEmbodiment 1 includes a substrate 10, a first conductor 20, a secondconductor 25, an insulating layer 40 and an adsorbent layer 30. Thesubstrate 10 has a plate-like shape, for example. The substrate 10 has,for example, a rectangular shape or a circular shape when viewed inplane. In the present embodiment, the substrate 10 has a circular shapewhen viewed in plane. Each of the first conductor 20 and the secondconductor 25 functions as an electrode.

The first conductor 20 is disposed on the substrate 10. A lower surfaceof the first conductor 20 is in contact with an upper surface of thesubstrate 10. The first conductor 20 has a shape that is notparticularly limited. The first conductor 20 has, for example, acircular arc shape or a ring shape when viewed in plane. In the presentembodiment, the first conductor 20 has a circular arc shape while havinga strip-like shape when viewed in plane. A center of a virtual circledetermined by a peripheral surface of the first conductor 20 may or maynot coincide with a center of gravity of a surface of the substrate 10(a center of the upper surface of the substrate 10). The ratio of adistance from the center of gravity of the surface of the substrate 10to the first conductor 20 to a radius of the surface of the substrate 10may be in a range of 0.1 to 0.8.

The first conductor 20 includes an exposed portion 20 a exposed to theoutside of the gas sensor 100. In FIG. 1, the exposed portion 20 aextends to the outside of the substrate 10 beyond a peripheral surfaceof the substrate 10. However, the first conductor 20 may not have aportion extending to the outside of the substrate 10 beyond theperipheral surface of the substrate 10. For example, the substrate 10may be provided with an opening so that a part of the lower surface ofthe first conductor 20 is exposed to the outside of the gas sensor 100through the opening. In this case, the part of the lower surface of thefirst conductor 20 corresponds to the exposed portion 20 a.

The second conductor 25 is disposed on the substrate 10. A lower surfaceof the second conductor 25 is in contact with the upper surface of thesubstrate 10. The second conductor 25 has a shape that is notparticularly limited. The second conductor 25 surrounds the firstconductor 20, for example. That is, the second conductor 25 may bepositioned outside of the first conductor 20 in a radial direction ofthe surface of the substrate 10. The second conductor 25 is out ofcontact with the first conductor 20. The second conductor 25 has, forexample, a circular arc shape or a ring shape when viewed in plane. Inthe present embodiment, the second conductor 25 has a circular arc shapewhile having a strip-like shape when viewed in plane. A center of avirtual circle determined by a peripheral surface of the secondconductor 25 may or may not coincide with the center of gravity of thesurface of the substrate 10. The center of the virtual circle determinedby the peripheral surface of the second conductor 25 may or may notcoincide with the center of the virtual circle determined by theperipheral surface of the first conductor 20. In the present embodiment,the first conductor 20 and the second conductor 25 are disposedconcentrically. The ratio of a distance from the center of gravity ofthe surface of the substrate 10 to the second conductor 25 to the radiusof the surface of the substrate 10 may be in a range of 0.2 to 0.9.

The second conductor 25 includes an exposed portion 25 a exposed to theoutside of the gas sensor 100. In FIG. 1, the exposed portion 25 aextends to the outside of the substrate 10 beyond the peripheral surfaceof the substrate 10. However, the second conductor 25 may not have aportion extending to the outside of the substrate 10 beyond theperipheral surface of the substrate 10. For example, the substrate 10may be provided with an opening so that a part of the lower surface ofthe second conductor 25 is exposed to the outside of the gas sensor 100through the opening. In this case, the part of the lower surface of thesecond conductor 25 corresponds to the exposed portion 25 a.

The insulating layer 40 covers each of the first conductor 20 and thesecond conductor 25. The insulating layer 40 is in contact with each ofthe first conductor 20 and the second conductor 25. The insulating layer40 may cover an entirety of the upper surface of the substrate 10. Theinsulating layer 40 may cover the upper surface of the substrate 10partially.

The insulating layer 40 has a first opening 45 and a second opening 46.The first opening 45 allows a part of a surface of the first conductor20 to be exposed therethrough. The first opening 45 overlaps with anupper surface of the first conductor 20. For example, an entirety of thefirst opening 45 overlaps with the first conductor 20 when viewed inplane. The first opening 45 extends through the insulating layer 40 in athickness direction thereof. The insulating layer 40, excluding thefirst opening 45, covers an entirety of the upper surface of the firstconductor 20 and an entirety of a side surface of the first conductor20.

The insulating layer 40 may have a plurality of the first openings 45.The number of the first openings 45 is not particularly limited. Thenumber of the first openings 45 may be in a range of 1 to 20, may be ina range of 2 to 8, may be in a range of 2 to 4, and may be in a range of2 to 3. In the present embodiment, the insulating layer 40 has the firstopenings 45 a, 45 b, 45 c and 45 d. The first openings 45 a, 45 b, 45 cand 45 d are arranged in a circular arc shape. In other words, the firstopenings 45 a, 45 b, 45 c and 45 d are arranged along a longitudinaldirection of the first conductor 20. To be specific, the first openings45 a, 45 b, 45 c and 45 d are arranged along a circumferential directionof the first conductor 20. In the present embodiment, the first openings45 a, 45 b, 45 c and 45 d are arranged along the circumferentialdirection of the first conductor 20 at equal intervals.

The second opening 46 allows a part of a surface of the second conductor25 to be exposed therethrough. The second opening 46 overlaps with anupper surface of the second conductor 25. For example, an entirety ofthe second opening 46 overlaps with the second conductor 25 when viewedin plane. The second opening 46 extends through the insulating layer 40in the thickness direction thereof. The insulating layer 40, excludingthe second opening 46, covers an entirety of the upper surface of thesecond conductor 25 and an entirety of a side surface of the secondconductor 25.

The insulating layer 40 may have a plurality of the second openings 46.The number of the second openings 46 is not particularly limited. Thenumber of the second openings 46 may be in a range of 1 to 20, may be ina range of 2 to 8, may be in a range of 2 to 4, and may be in a range of2 to 3. The number of the second openings 46 may be equal to ordifferent from the number of the first openings 45. In the presentembodiment, the insulating layer 40 has the second openings 46 a, 46 b,46 c and 46 d. The second openings 46 a, 46 b, 46 c and 46 d arearranged in a circular arc shape. In other words, the second openings 46a, 46 b, 46 c and 46 d are arranged along a longitudinal direction ofthe second conductor 25. To be specific, the second openings 46 a, 46 b,46 c and 46 d are arranged along a circumferential direction of thesecond conductor 25. In the present embodiment, the second openings 46a, 46 b, 46 c and 46 d are arranged along the circumferential directionof the second conductor 25 at equal intervals.

The first opening 45 and the second opening 46 each has a shape that isnot particularly limited. Each of the first opening 45 and the secondopening 46 has, for example, a circular shape or a rectangular shapewhen viewed in plane. Each of the first opening 45 and the secondopening 46 may have an area in a range of 0.2 to 200000 μm², in a rangeof 0.2 to 2000 μm², and in a range of 15 to 25 μm² when viewed in plane.In this case, since the number of the electric current paths in theadsorbent layer 30 is sufficiently small, the electric resistance of theadsorbent layer 30 changes more significantly due to the change in theelectric current paths. Thereby, a gas can be detected more reliably.Moreover, an electric current passes easily to the adsorbent layer 30from the first conductor 20 or the second conductor 25. Thereby, theelectric resistance of the adsorbent layer 30 can be measured easily. Inthe case where each of the first opening 45 and the second opening 46has a circular shape when viewed in plane, each of the first opening 45and the second opening 46 may have a diameter in a range of 0.5 to 500μm, in a range of 0.5 to 50 μm, and in a range of 4.37 to 5.64 μm. Thearea and the diameter of the first opening 45 and the second opening 46when viewed in plane can be measured by observing a surface of theinsulating layer 40 with an electron microscope.

The adsorbent layer 30 is in contact with the first conductor 20 and thesecond conductor 25 respectively through the first opening 45 and thesecond opening 46. For example, as shown in FIG. 1 and FIG. 2, theadsorbent layer 30 is in contact with the first conductor 20 through thefirst opening 45 c. The adsorbent layer 30 is in contact with the secondconductor 25 through the second opening 46 c. Therefore, an electriccurrent passes to the adsorbent layer 30 when a voltage is applied tothe first conductor 20 and the second conductor 25. Thereby, theelectric resistance of the adsorbent layer 30 can be measured. Theadsorbent layer 30 is disposed on the insulating layer 40. The adsorbentlayer 30 covers an entirety of an upper surface of the insulating layer40 and an entirety of a side surface of the insulating layer 40. Theadsorbent layer 30 may cover the upper surface and the side surface ofthe insulating layer 40 only partially. The adsorbent layer 30 may coverthe entirety of the upper surface of the substrate 10, and may cover theupper surface of the substrate 10 partially. The adsorbent layer 30 mayor may not be in contact with the substrate 10.

The adsorbent layer 30 has a thickness that is determined in accordancewith the type of a gas to be detected, the composition of the adsorbentlayer 30, etc. The thinner the adsorbent layer 30 is, the more stablythe electric resistance of the adsorbent layer 30 can be measured. Thethickness of the adsorbent layer 30 may be in a range of 0.1 to 10 μm.The adsorbent layer 30 has a shape that is not particularly limited. Theadsorbent layer 30 has, for example, a circular shape or a ring shapewhen viewed in plane. In this embodiment, the adsorbent layer 30 has aring shape when viewed in plane. The adsorbent layer 30 has an area in arange of, for example, 0.002 to 50 mm² when viewed in plane.

As shown in FIG. 3, in the present embodiment, the first openings 45 a,45 b, 45 c and 45 d are positioned on a virtual circle C2 that is in aconcentric relationship with a virtual circle C1 determined by an outerperiphery 30 a of the adsorbent layer 30 when the adsorbent layer 30 isviewed in plane. In FIG. 3, the first conductor 20 and the secondconductor 25 are omitted for convenience. The first openings 45 a, 45 b,45 c and 45 d are arranged along the virtual circle C2 at equiangularintervals.

In the present embodiment, when the adsorbent layer 30 is viewed inplane, the second openings 46 a, 46 b, 46 c and 46 d are positioned on avirtual circle C3 that is in a concentric relationship with the virtualcircle C1. The virtual circle C3 is different from the virtual circleC2. The second openings 46 a, 46 b, 46 c and 46 d are arranged along thevirtual circle C3 at equiangular intervals.

In the present embodiment, the first openings 45 a and 45 c and thesecond openings 46 a and 46 c are positioned on a virtual straight lineL1. The first openings 45 b and 45 d and the second openings 46 b and 46d are positioned on a virtual straight line L2. Each of the virtualstraight line L1 and the virtual straight line L2 extends radially froma center O of the virtual circle C1. The virtual straight line L1 isorthogonal to the virtual straight line L2.

As shown in FIG. 1, the gas sensor 100 may further be provided with afirst wall 11. The first wall 11 surrounds the surface of the substrate10. The first wall 11 has a ring shape when viewed in plane. The firstwall 11 extends upward (in a thickness direction of the substrate 10)from the substrate 10. The surface of the substrate 10 surrounded by thefirst wall 11 has a circular shape, for example. The first wall 11 isjoined to an outer periphery of the substrate 10. The first wall 11 maybe integrated with the substrate 10. In other words, the first wall 11may be a part of the substrate 10. The first wall 11 extends upwardhigher than the adsorbent layer 30. The first wall 11 has an innerperipheral surface that is in contact with the adsorbent layer 30.

The gas sensor 100 may further be provided with a second wall 12. Thesecond wall 12 extends upward from a part of the surface of thesubstrate 10. The second wall 12 has, for example, a circular columnshape or a cylindrical shape. The second wall 12 is joined to the partof the surface of the substrate 10. The second wall 12 may be integratedwith the substrate 10. In other words, the second walls 12 may be a partof the substrates 10. The second wall 12 is surrounded by the firstconductor 20. The second wall 12 has an outer peripheral surface thatsurrounds the center of gravity of the surface of the substrate 10. Thesecond wall 12 extends upward higher than the adsorbent layer 30. Theouter peripheral surface of the second wall 12 is in contact with theadsorbent layer 30. The adsorbent layer 30 is disposed between the firstwall 11 and the second wall 12.

A material of the substrate 10 is not particularly limited as long as itallows a shape of the gas sensor 100 to be maintained. Examples of thesubstrate 10 include an Si substrate, a metal plate, a glass plate and ahigh polymer film.

A material of the first conductor 20 and a material of the secondconductor 25 are not particularly limited as long as they can be appliedwith a voltage. The first conductor 20 and the second conductor 25 eachcontain, for example, at least one metal selected from the groupconsisting of silver, gold, copper, platinum and aluminum. The materialof the first conductor 20 may be the same as the material of the secondconductor 25.

A material of the insulating layer 40 is not particularly limited aslong as it has an insulating property. The material of the insulatinglayer 40 contains, for example, at least one selected from the groupconsisting of an insulating polymer material, ceramics and glass. Theinsulating polymer material contains, for example, at least one selectedfrom the group consisting of polyethylene, polypropylene, polystyrene,polybutadiene, an epoxy resin, a fluororesin, polyvinyl chloride,polymethyl methacrylate, polyamide, polyimide, polycarbonate, celluloseacetate, polyethylene terephthalate, polyethylene naphthalate, polyethersulphone, polyphenylene sulfide and polyether imide. The ceramicscontains, for example, at least one selected from the group consistingof SiO₂, Si₃N₄, Al₂O₃, Zr₂O₃ and MgO.

The adsorbent layer 30 contains a conductive material and an organicadsorbent. Since the adsorbent layer 30 contains the conductivematerial, it is possible to pass an electric current through theadsorbent layer 30. By passing an electric current through the adsorbentlayer 30, it is possible to measure the electric resistance of theadsorbent layer 30. The conductive material is not particularly limitedas long as it has conductivity. The conductive material contains, forexample, at least one selected from the group consisting of a carbonmaterial, a conductive polymer, a metal material, a metal oxide, asemiconductor material, a superconductor and a complex compound.

The carbon material contains, for example, at least one selected fromthe group consisting of carbon black, graphite, coke, carbon nanotube,graphene and fulleren. The conductive polymer contains, for example, atleast one selected from the group consisting of polyaniline,polythiophene, polypyrrole and polyacethylene. The metal materialcontains, for example, at least one selected from the group consistingof silver, gold, copper, platinum and aluminum. The metal oxidecontains, for example, at least one selected from the group consistingof an indium oxide, a tin oxide, a tungstic oxide, a zinc oxide and atitanium oxide. The semiconductor material contains, for example, atleast one selected from the group consisting of silicon, galliumarsenide, indium phosphide and molybdenum sulfide. The superconductorcontains, for example, at least one selected from the group consistingof YBa₂Cu₃O₇ and Tl₂Ba₂Ca₂Cu₃O₁₀. The complex compound contains, forexample, at least one selected from the group consisting of a complexcompound of tetramethylparaphenylenediamine and chloranil, a complexcompound of tetracyanoquinodimethane and an alkali metal, a complexcompound of tetrathiafulvalene and halogen, a complex compound ofiridium and a halocarbonyl compound, and tetracyanoplatinum.

Typically, the conductive material contains carbon black. In the casewhere the conductive material contains carbon black, the electricresistance of the adsorbent layer changes more significantly. Therefore,a gas can be detected more reliably.

Typically, the adsorbent layer 30 contains particles of the conductivematerial. The particles of the conductive material may have an averageparticle diameter in a range of 10 to 300 nm. The “average particlediameter” can be measured by the following method. A surface or a crosssection of the adsorbent layer 30 is observed with an electronmicroscope, and an arbitrary number (50, for example) of the particlescontained in the adsorbent layer 30 are measured for diameter. Anaverage calculated using the measurements obtained is determined as theaverage particle diameter. A diameter of a circle having an area equalto that of a particle observed with an electron microscope can beregarded as a particle diameter.

A ratio of a weight of the conductive material to a weight of theadsorbent layer 30 may be in a range of 0.05 to 0.95, and may be in arange of 0.25 to 0.95. The ratio of the weight of the conductivematerial to the weight of the adsorbent layer 30 may be 0.5. In the casewhere the conductive material is carbon black, a ratio of a weight ofthe carbon black to the weight of the adsorbent layer 30 may be in arange of 0.25 to 0.95. In this case, an electric current passes easilyto the adsorbent layer 30 from the first conductor 20 or the secondconductor 25. Thereby, the electric resistance of the adsorbent layer 30can be measured easily.

The organic adsorbent can adsorb a gas. The organic adsorbent adsorbs agas, so that the adsorbent layer 30 changes in volume. A material of theorganic adsorbent is determined in accordance with the type of a gas tobe detected, the type of the conductive material, etc. Examples of thematerial of the organic adsorbent include a material marketed as astationary phase in a column used for gas chromatography. The materialof the organic adsorbent contains, for example, at least one selectedfrom the group consisting of a polymer material and a low-molecularmaterial. The organic adsorbent contains, for example, at least oneselected from the group consisting of polyalkylene glycols, polyesters,silicones, glycerols, nitriles, dicarboxylic acid monoesters andaliphatic amines. In this case, the organic adsorbent can adsorb a gaseasily.

The polyalkylene glycols include polyethylene glycol, for example. Thepolyesters include, for example, at least one selected from the groupconsisting of poly(diethylene glycol adipate) and poly(ethylenesuccinate). The silicones include, for example, at least one selectedfrom the group consisting of dimethyl silicone, phenylmethyl silicone,trifluoropropyl methyl silicone and cyano silicone. The glycerolsinclude diglycerol, for example. The nitriles include, for example, atleast one selected from the group consisting ofN,N-bis(2-cyanoethyl)formamide and 1,2,3-tris(2-cyanoethoxy)propane. Thedicarboxylic acid monoesters include, for example, at least one selectedfrom the group consisting of nitroterephthalic acid modifiedpolyethylene glycol and diethylene glycol succinate. The aliphaticamines include tetrahydroxyethyl ethylenediamine, for example.

A ratio of a weight of the organic adsorbent to the weight of theadsorbent layer 30 is determined in accordance with the type of a gas tobe detected, the type of the conductive material, etc. The ratio of theweight of the organic adsorbent to the weight of the adsorbent layer 30may be in a range of 0.05 to 0.95.

The adsorbent layer 30 may further contain an additive. Examples of theadditive include a dispersant.

A material of the first wall 11 and a material of the second wall 12each are not particularly limited. Each of the material of the firstwall 11 and the material of the second wall 12 may have hydrophobicity.Each of the material of the first wall 11 and the material of the secondwall 12 contains a hydrophobic polymer material, for example. Thehydrophobic polymer material contains, for example, at least oneselected from the group consisting of polyethylene, polypropylene,polystyrene, polybutadiene, an epoxy resin and a fluororesin. Thematerial of the first wall 11 may be the same as the material of thesecond wall 12. The material of the first wall 11 and the material ofthe second wall 12 each may be the same as the material of the substrate10.

Next, a method for manufacturing the gas sensor 100 is described.

First, each of the first conductor 20 and the second conductor 25 isdisposed on the substrate 10. A method for disposing each of the firstconductor 20 and the second conductor 25 on the substrate 10 is notparticularly limited. For example, it is possible to dispose each of thefirst conductor 20 and the second conductor 25 on the substrate 10 bydepositing metal on the substrate 10. As a method for depositing themetal, there can be mentioned, for example, a sputtering method, an ionplating method, an electron beam evaporation method, a vacuumevaporation method, a chemical evaporation method and a chemical vapordeposition method.

Next, the insulating layer 40 is produced. A method for producing theinsulating layer 40 is not particularly limited. The insulating layer 40can be produced by the following method, for example. A dispersionliquid containing the insulating polymer material is prepared. Thedispersion liquid is obtained by dispersing the insulating polymermaterial in a coating solvent. Examples of the coating solvent includeat least one selected from the group consisting of water and an organicsolvent.

The dispersion liquid is applied, in a desired pattern, to each of thefirst conductor 20 and the second conductor 25 to form a coating film.As a method for forming the coating film, a printing method can bementioned. The coating film is dried, so that a precursor layer of theinsulating layer 40 is formed.

Next, the first opening 45 and the second opening 46 are formed in theprecursor layer of the insulating layer 40. Thereby, the insulatinglayer 40 can be produced. A method for forming the first opening 45 andthe second opening 46 is not particularly limited. The first opening 45and the second opening 46 can be formed by, for example, irradiating theprecursor layer of the insulating layer 40 with an ion beam. The firstopening 45 and the second opening 46 can also be formed by, for example,etching the precursor layer of the insulating layer 40.

Next, the adsorbent layer 30 is produced. First, a dispersion liquidcontaining the conductive material and the organic adsorbent isprepared. The dispersion liquid is obtained by dispersing the conductivematerial and the organic adsorbent in a coating solvent. Examples of thecoating solvent include at least one selected from the group consistingof water and an organic solvent. Next, the dispersion liquid is appliedto the insulating layer 40 to form a coating film. The coating film isdried, so that the adsorbent layer 30 is formed.

The adsorbent layer 30 formed by the above-mentioned method usually hasa thickness that is uniform in a circumferential direction of thesurface of the substrate 10. In the gas sensor 100 of the presentembodiment, each of the first conductor 20 and the second conductor 25has a circular arc shape or a ring shape when viewed in plane.Therefore, the adsorbent layer 30 has a thickness that is uniform alongthe first conductor 20. Similarly, the adsorbent layer 30 has athickness that is uniform along the second conductor 25. In this case,the electric resistance of the adsorbent layer 30 can be measuredstably.

In the case where the gas sensor 100 is provided with the first wall 11and the second wall 12, the dispersion liquid can be applied uniformly.That is, it is possible for the adsorbent layer 30 to have a uniformthickness. In the case where each of the first wall 11 and the secondwall 12 has hydrophobicity, a surface tension generated between thedispersion liquid and the first wall 11 and that generated between thedispersion liquid and the second wall 12 are low. This makes it possiblefor the adsorbent layer 30 to have a more uniform thickness.

Next, a method for detecting a gas using the gas sensor 100 isdescribed.

First, each of the exposed portion 20 a of the first conductor 20 andthe exposed portion 25 a of the second conductor 25 is connected to adetector. The detector can apply a voltage to the first conductor 20 andthe second conductor 25. When a voltage is applied to the firstconductor 20 and the second conductor 25, an electric current passesthrough the adsorbent layer 30. The detector can measure the electricresistance of the adsorbent layer 30 based on the electric currentpassing through the adsorbent layer 30.

Next, the gas sensor 100 is placed under an atmosphere containing a gas.The gas contains a volatile organic compound, for example. The volatileorganic compound contains, for example, at least one selected from thegroup consisting of ketones, amines, alcohols, aromatic hydrocarbons,aldehydes, esters, organic acid, hydrogen sulfide, methyl mercaptan,disulfide and pyrrole.

When the gas comes in contact with the gas sensor 100, the organicadsorbent contained in the adsorbent layer 30 adsorbs the gas. When theorganic adsorbent adsorbs the gas, the adsorbent layer 30 changes involume. To be specific, the adsorbent layer 30 expands or shrinks. Thechange in the volume of the adsorbent layer 30 changes the positionalrelationship between the conductive materials in the adsorbent layer 30.In the gas sensor 100, the first conductor 20 has a surface that iscovered with the insulating layer 40, and no electric current passesfrom that surface to the adsorbent layer 40. The second conductor 25 hasa surface that is covered with the insulating layer 40, and no electriccurrent passes from that surface to the adsorbent layer 30. That is, thenumber of the electric current paths in the adsorbent layer 30 is small.Therefore, the electric current paths change significantly due to thechange in the positional relationship between the conductive materials.The significant change in the electric current paths changes theelectric resistance of the adsorbent layer 30 significantly. Thesignificant change in the electric resistance of the adsorbent layer 30makes it possible to detect a gas more reliably. According to the gassensor 100 of the present embodiment, it is possible to detect a gaseven in the case where the gas has a concentration in a range of 0.1 to1000 ppm.

In the present embodiment, the adsorbent layer 30 has a ring shape whenviewed in plane. Therefore, when the adsorbent layer 30 adsorbs the gas,the adsorbent layer 30 expands or shrinks to a radial direction of thevirtual circle C1. The first openings 45 a, 45 b, 45 c and 45 d arepositioned on the virtual circle C2. Furthermore, the second openings 46a, 46 b, 46 c and 46 d are positioned on the virtual circle C3. Sincethe virtual circles C1, C2 and C3 are in a concentric relationship witheach other, the variation in the change in the electric current paths isinhibited when the adsorbent layer 30 expands or shrinks. Particularly,in the present embodiment, since the first openings 45 a, 45 b, 45 c and45 d, and the second openings 46 a, 46 b, 46 c and 46 d are positionedon the virtual straight line L1 or the virtual straight line L2, thevariation in the change in the electric current paths is more inhibited.This makes it possible to detect stably the change in the electricresistance of the adsorbent layer 30 caused by the change in theelectric current paths. Thereby, the gas sensor 100 can detect a gasstably.

Next, a gas sensor assembly according to the present embodiment isdescribed.

As shown in FIG. 4, a gas sensor assembly 200 is provided with aplurality of the gas sensors 100 and a substrate 210. The substrate 210has a plate-like shape, for example. The substrate 210 has, for example,a rectangular shape when viewed in plane. The substrate 210 has twopairs of end faces; one pair of end faces face each other, and the otherpair of end faces face each other.

Each of the gas sensors 100 is disposed on the substrate 210. Each ofthe gas sensors 100 is connected to a detector (not shown). Therespective adsorbent layers 30 of at least two selected from the gassensors 100 may be composed of the same material. In this case, the gassensor assembly 200 has higher detection accuracy against a specificgas. The respective adsorbent layers 30 of at least two selected fromthe gas sensors 100 may be composed of different materials,respectively. The adsorbent layers 30 of the gas sensors 100 may containthe different organic adsorbents, respectively. In this case, the gassensors 100 respectively exhibit different behaviors against a specificgas. For example, a gas that is unlikely to be adsorbed by a specificone of the specific gas sensors 100 is adsorbed by one of the other gassensors 100. Thereby, the gas sensor assembly 200 can detect a mixed gascontaining a plurality of gases.

The number of the gas sensors 100 that the gas sensor assembly 200 hasis not particularly limited. The number of the gas sensors 100 is 16,for example. In FIG. 4, four units of the gas sensors 100 are arrangedin a direction from one end face toward the other end face of one of thepairs of the end faces of the substrate 210. Four units of the gassensors 100 are arranged in a direction from one end face toward theother end face of the other pair of the end faces of the substrate 210.

Modification of Embodiment 1

The surface of the substrate 10 surrounded by the first wall 11 may nothave a circular shape. In a gas sensor 110 in FIG. 5, the first wall 11includes a plurality of projecting portions 11 a. Each of the projectingportions 11 a projects from the outer periphery of the substrate 10toward the center of gravity of the surface of substrate 10. Each of theprojecting portions 11 a has a fan shape when viewed in plane. Thesurface of the substrate 10 surrounded by the first wall 11 has a gearshape, for example. The number of the projecting portions 11 a is notparticularly limited. The number of the projecting portions 11 a is 6,for example. In FIG. 5, each of the projecting portions 11 a is out ofcontact with the second wall 12. However, each of the projectingportions 11 a may be in contact with the second wall 12.

As shown in FIG. 6, each of the projecting portions 11 a coverspartially the upper surface and the side surface of the first conductor20. Each of the projecting portions 11 a covers partially the uppersurface and the side surface of the second conductor 25. Each of theprojecting portions 11 a is in contact with the first conductor 20 andthe second conductor 25. The first conductor 20 has portions that arecovered respectively with the projecting portions 11 a and that are outof contact with the insulating layer 40 and the adsorbent layer 30. Thesecond conductor 25 has portions that are covered respectively with theprojecting portions 11 a and that are out of contact with the insulatinglayer 40 and the adsorbent layer 30. However, the portions that thefirst conductor 20 has and that are covered respectively with theprojecting portions 11 a and the portions that the second conductor 25has and that are covered respectively with the projecting portions 11 amay be covered with the insulating layer 40.

As shown in FIG. 5, a detecting section 35 is formed between twoprojecting portions 11 a adjacent to each other in the circumferentialdirection of the surface of the substrate 10. The gas sensor 110typically has the same number of the detecting sections 35 as the numberof the projecting portions 11 a. In each of the detecting sections 35,the insulating layer 40 covers each of the first conductor 20 and thesecond conductor 25. The insulating layer 40 has one first opening 45and one second opening 46 in one detecting section 35. In one detectingsection 35, the adsorbent layer 30 is in contact with the firstconductor 20 and the second conductor 25 respectively through the firstopening 45 and the second opening 46. In each of the detecting sections35, the electric resistance of the adsorbent layer 30 can be measured.

In the production of the adsorbent layer 30 of the gas sensor 110, thedispersion liquid can be applied more uniformly in each of the detectingsections 35. That is, it is possible for the adsorbent layer 30 to havea more uniform thickness in the gas sensor 110.

Embodiment 2

The first conductor 20 may not have a circular arc shape or a ring shapewhen viewed in plane. Also, the second conductor 25 may not surround thefirst conductor 20. Furthermore, the adsorbent layer 30 may not have acircular shape or a ring shape when viewed in plane. In a gas sensor 120in FIG. 7, the first conductor 20 has a rectangular shape as well as astrip-like shape when viewed in plane. The second conductor 25 has arectangular shape as well as a strip-like shape when viewed in plane.The adsorbent layer 30 has a rectangular shape when viewed in plane. Inthe present embodiment, the adsorbent layer 30 has a strip-like shape.The substrate 10 has a rectangular shape when viewed in plane. The gassensor 120 is not provided with the second wall 12. The gas sensor 120has a structure identical to that of the gas sensor 100 of Embodiment 1except the shape of the first conductor 20, the shape of the secondconductor 25, the shape of the adsorbent layer 30, the shape of thesubstrate 10, and the presence or absence of the second wall 12.Therefore, elements that are common between the gas sensor 100 ofEmbodiment 1 and the gas sensor 120 of the present embodiment aredesignated by the same reference numerals and the descriptions thereofmay be omitted. That is, the descriptions about each of the followingembodiments may be applied interchangeably unless they are technicallycontradictory. Furthermore, the embodiments may be used in combinationunless they are technically contradictory.

A plurality of outlines 30 b, 30 c, 30 d and 30 e constitute the outerperiphery 30 a of the adsorbent layer 30. The outlines 30 b and 30 dface each other. The outlines 30 c and 30 e face each other. Each of theoutlines 30 c and 30 e extends in a first direction X. Each of theoutlines 30 b and 30 d extends in a second direction Y. The firstdirection X is orthogonal to the second direction Y.

Each of the first conductor 20 and the second conductor 25 extends inthe second direction Y. The first conductor 20 and the second conductor25 are arranged in the first direction X.

The first openings 45 a, 45 b, 45 c and 45 d are arranged linearly alongthe second direction Y. In other words, the first openings 45 a, 45 b,45 c and 45 d are arranged along a longitudinal direction of the firstconductor 20. In the present embodiment, the first openings 45 a, 45 b,45 c and 45 d are arranged along the second direction Y at equalintervals.

The second openings 46 a, 46 b, 46 c and 46 d are arranged linearlyalong the second direction Y. In other words, the second openings 46 a,46 b, 46 c and 46 d are arranged along a longitudinal direction of thesecond conductor 25. In the present embodiment, the second openings 46a, 46 b, 46 c and 46 d are arranged along the second direction Y atequal intervals. At least one selected from the first openings 45 and atleast one selected from the second openings 46 may be arranged along thefirst direction X. In the present embodiment, the first opening 45 a andthe second opening 46 a are arranged along the first direction X. Thefirst opening 45 b and the second opening 46 b are arranged along thefirst direction X. The first opening 45 c and the second opening 46 care arranged along the first direction X. The first opening 45 d and thesecond opening 46 d are arranged along the first direction X.

The gas sensor 120 of the present embodiment is not provided with thesecond wall 12. However, the gas sensor 120 may be provided with thesecond wall 12. In this case, the second wall 12 may have a prism shape.In the case where the gas sensor 120 is provided with the second wall12, the adsorbent layer 30 has a frame shape when viewed in plane.

In the present embodiment, the adsorbent layer 30 has a rectangularshape when viewed in plane. Therefore, when the adsorbent layer 30adsorbs a gas, the adsorbent layer 30 expands or shrinks in the firstdirection X as well as in the second direction Y. Also, the adsorbentlayer 30 expands or shrinks in a direction opposite to the firstdirection X as well as in a direction opposite to the second directionY. The first openings 45 a, 45 b, 45 c and 45 d are arranged along thesecond direction Y. Furthermore, the second openings 46 a, 46 b, 46 cand 46 d are also arranged along the second direction Y. Therefore, thevariation in the change in the electric current paths is inhibited whenthe adsorbent layer 30 expands or shrinks. This makes it possible todetect stably the change in the electric resistance of the adsorbentlayer 30 caused by the change in the electric current paths. Thereby,the gas sensor 100 can detect a gas stably.

Embodiment 3

The gas sensor 120 of Embodiment 2 may be provided with a plurality ofthe first conductors 20 and a plurality of the second conductors 25.Each of the first conductors 20 may have one first opening 45. Each ofthe second conductors 25 may have one second opening 46. In a gas sensor130 in FIG. 8, each of the first conductors 20 extends in the seconddirection Y. The first conductors 20 are connected electrically to eachother with a wiring 50. The number of the first conductors 20 may be ina range of 2 to 10.

Each of the second conductors 25 extends in the direction opposite tothe second direction Y. The second conductors 25 are connectedelectrically to each other with a wiring 55. The first conductors 20 andthe second conductors 25 are arranged alternately in the first directionX. The number of the first conductors 25 may be in a range of 2 to 10.

The first openings 45 a, 45 b, 45 c and 45 d are arranged linearly alongthe first direction X. In the present embodiment, the first openings 45a, 45 b, 45 c and 45 d are arranged along the first direction X at equalintervals. The second openings 46 a, 46 b, 46 c and 46 d are arrangedlinearly along the first direction X. In the present embodiment, thesecond openings 46 a, 46 b, 46 c and 46 d are arranged along the firstdirection X at equal intervals.

In the present embodiment, the adsorbent layer 30 has a rectangularshape when viewed in plane. Therefore, when the adsorbent layer 30adsorbs a gas, the adsorbent layer 30 expands or shrinks in the firstdirection X as well as in the second direction Y. Also, the adsorbentlayer 30 expands or shrinks in the direction opposite to the firstdirection X as well as in the direction opposite to the second directionY. The first openings 45 a, 45 b, 45 c and 45 d are arranged along thefirst direction X. Furthermore, the second openings 46 a, 46 b, 46 c and46 d are also arranged along the first direction X. Therefore, thevariation in the change in the electric current paths is inhibited whenthe adsorbent layer 30 expands or shrinks. This makes it possible todetect stably the change in the electric resistance of the adsorbentlayer 30 caused by the change in the electric current paths. Thereby,the gas sensor 100 can detect a gas stably.

The adsorbent layer 30 may not have the shapes indicated in Embodiments1 to 3. The adsorbent layer 30 may have a wire-like shape, a fence-like,or a mesh-like shape. In this case, the adsorbent layer 30 coverspartially each of the first conductor 20 and the second conductor 25.Therefore, even in the case where the gas sensor is not provided withthe insulating layer 40, the number of the electric current paths in theadsorbent layer 30 is small. According to the adsorbent layer 30 thusprovided, the electric resistance of the adsorbent layer 30 changessignificantly even in the case where the gas sensor is not provided withthe insulating layer 40. Thereby, a gas can be detected more reliably.

EXAMPLES

The present disclosure is described in detail with reference toexamples. However, the present disclosure is not limited in any way bythe following examples.

(Sample 1)

First, the first conductor and the second conductor each were disposedon the substrate. Each of the first conductor and the second conductorwas made of platinum. The Si substrate was used as the substrate. Eachof the first conductor and the second conductor had a circular arc shapewhen viewed in plane. The second conductor surrounded the firstconductor.

Next, each of the first conductor and the second conductor was coveredwith the precursor layer of the insulating layer. The precursor layerwas made of SiO₂. The precursor layer was provided with one firstopening and one second opening so as to produce the insulating layer.Each of the first opening and the second opening had a circular shapewhen viewed in plane. Each of the first opening and the second openinghad a diameter of 5 μm when viewed in plane. That is, each of the firstopening and the second opening had an area of 20 μm².

Next, the insulating layer was applied with the dispersion liquidcontaining the conductive material and the organic adsorbent to form thecoating film. Carbon black was used as the conductive material.Polyethylene glycol was used as the organic adsorbent. The coating filmwas dried to form the adsorbent layer. The ratio of the weight of theconductive material to the weight of the adsorbent layer was 0.5. Theadsorbent layer had a ring shape when viewed in plane. Thus, a gassensor of Sample 1 was obtained.

(Sample 2)

A gas sensor of Sample 2 was obtained by the same method as that ofExample 1, except that the precursor layer of the insulating layer wasprovided with four first openings and four second openings so as toproduce the insulating layer.

(Sample 3)

A gas sensor of Sample 3 was obtained by the same method as that ofExample 1, except that the precursor layer of the insulating layer wasprovided with eight first openings and eight second openings so as toproduce the insulating layer.

(Sample 4)

A gas sensor of Sample 4 was obtained by the same method as that ofExample 1, except that the precursor layer of the insulating layer wasprovided with 16 first openings and 16 second openings so as to producethe insulating layer.

(Sample 5)

A gas sensor of Sample 5 was obtained by the same method as that ofExample 1, except that the insulating layer was not produced.

(Measurement of the Rate of Change in Electric Resistance)

Samples 1 to 5 were placed under an atmosphere containing gaseousnonanal, and the adsorbent layer of each of Samples 1 to 5 was measuredfor the rate of change in electric resistance. The electric resistanceof the adsorbent layer before the adsorbent layer adsorbed nonanal wasdefined as R₁. The electric resistance of the adsorbent layer after theadsorbent layer adsorbed nonanal was defined as R₂. The differencebetween R₁ and R₂ was defined as ΔR. A rate C (%) of change in electricresistance was a value calculated by ΔR/R₁×100. The nonanal had aconcentration of 0.8 ppm.

As shown in FIG. 9, the gas sensors of Samples 1 to 4 had a rate C ofchange higher than that of the gas sensor of Sample 5. The horizontalaxis of the graph in FIG. 9 indicates the number of the first openings.With the rate C of change of Sample 5, the gas fails to be detected insome cases. As can be seen from FIG. 9, the gas sensors of the presentembodiments can detect the gas more reliably.

The smaller the number of the first openings and the number of thesecond openings are, the smaller the number of the electric currentpaths in the adsorbent layer becomes. The graph in FIG. 9 indicates thatthe smaller the number of the electric current paths in the adsorbentlayer is, the higher the rate C of change in the electric resistance ofthe adsorbent layer becomes. On the other hand, however, the value ofthe rate C of change decreased when the number of the first openings andthe number of the second openings are less than a specific value, as canbe seen from the measurement result of Sample 1.

(Sample 6)

A gas sensor of Sample 6 was obtained by the same method as that ofExample 1, except that: four conductors having a rectangular shape whenviewed in plane were used as the first conductors and four conductorshaving a rectangular shape when viewed in plane were used as the secondconductors; the first conductors and the second conductors were arrangedalternately in a direction orthogonal to a thickness direction of thesubstrate; each of the first conductors was provided with one firstopening; each of the second conductors was provided with one secondopening; and the adsorbent layer had a rectangular shape when viewed inplane.

(Sample 7)

A gas sensor of Sample 7 was obtained by the same method as that ofExample 6, except that: one conductor having a rectangular shape whenviewed in plane was used as the first conductor and one conductor havinga rectangular shape when viewed in plane was used as the secondconductor; the first conductor was provided with four first openings;and the second conductor was provided with four second openings.

(Measurement of the Rate of Change in Electric Resistance)

Samples 2, 6 and 7 were placed under an atmosphere containing gaseousnonanal, and the adsorbent layer of each of Samples 2, 6 and 7 wasmeasured for the rate C (%) of change in electric resistance. Thenonanal had a concentration of 0.8 ppm.

As shown in FIG. 10, the gas sensor of Sample 2 had a rate C of changehigher than those of the other gas sensors. This result reveals that thegas sensor can detect the gas more reliably when the conditions that theadsorbent layer has a ring shape when viewed in plane, the firstopenings are arranged in a circular arc shape, and the second openingsare arranged in a circular arc shape are satisfied.

INDUSTRIAL APPLICABILITY

The technology disclosed in the present description is useful fordetection of a gas, etc.

1. A gas sensor comprising: a substrate; a first conductor and a second conductor that are disposed on the substrate; an insulating layer that covers the first conductor and the second conductor, and that has a first opening that allows a part of a surface of the first conductor to be exposed therethrough and a second opening that allows a part of a surface of the second conductor to be exposed therethrough; and an adsorbent layer that contains a conductive material and an organic adsorbent that can adsorb a gas, and that is in contact with the first conductor and the second conductor respectively through the first opening and the second opening.
 2. The gas sensor according to claim 1, wherein the insulating layer has a plurality of the first openings and a plurality of the second openings.
 3. The gas sensor according to claim 2, wherein the first openings are arranged in a circular arc shape and the second openings are arranged in a circular arc shape.
 4. The gas sensor according to claim 3, wherein the adsorbent layer has a circular shape or a ring shape when viewed in plane, the first openings are positioned on a virtual circle that is in a concentric relationship with a virtual circle determined by an outer periphery of the adsorbent layer when the adsorbent layer is viewed in plane, and the second openings are positioned on a virtual circle that is in a concentric relationship with the virtual circle determined by the outer periphery of the adsorbent layer.
 5. The gas sensor according to claim 4, wherein one selected from the first openings and one selected from the second openings are positioned on one of a plurality of virtual straight lines extending radially from a center of the virtual circle determined by the outer periphery of the adsorbent layer.
 6. The gas sensor according to claim 2, wherein the first openings are arranged linearly and the second openings are arranged linearly.
 7. The gas sensor according to claim 6, wherein the adsorbent layer has a rectangular shape when viewed in plane, the first openings are arranged along a direction in which at least one selected from a plurality of outlines constituting an outer periphery of the adsorbent layer extends when the adsorbent layer is viewed in plane, and the second openings are arranged along a direction in which the first openings are arranged.
 8. The gas sensor according to claim 1, wherein an entirety of the first opening overlaps with the first conductor when viewed in plane, and an entirety of the second opening overlaps with the second conductor when viewed in plane.
 9. The gas sensor according to claim 1, wherein the organic adsorbent contains at least one selected from the group consisting of polyalkylene glycols, polyesters, silicones, glycerols, nitriles, dicarboxylic acid monoesters and aliphatic amines.
 10. The gas sensor according to claim 1, wherein the conductive material contains carbon black.
 11. The gas sensor according to claim 10, wherein a ratio of a weight of the carbon black to a weight of the adsorbent layer is in a range of 0.25 to 0.95.
 12. The gas sensor according to claim 1, wherein each of the first opening and the second opening has an area in a range of 0.2 to 2000 μm² when viewed in plane.
 13. The gas sensor according to claim 1, wherein each of the first opening and the second opening has a circular shape when viewed in plane, and each of the first opening and the second opening has a diameter in a range of 0.5 to 50 μm. 